**【报告题目】****Quantum criticality of the Rabi-Stark model at finite frequency ratios**

**【报告人】陈庆虎 教授，浙江大学**

**【报告时间】****2020.12.02 (****周三****) ****下午 ****14: 00**

**【地点】科技楼 ****29#-414**

**【报告摘要】**In this talk, we analyze the quantum criticality of the Rabi-Stark model at finite ratios of the qubit and cavity frequencies in terms of the energy gap, the order parameter, as well as the fidelity, if the Stark coupling strength is the same as the cavity frequency. The critical exponents are derived analytically. The energy gap and the length critical exponents are different from those in the quantum Rabi model and the Dicke model. The finite size scaling analysis for the order parameter and the fidelity susceptibility is also performed. Interestingly, the universal scaling behaviors are demonstrated and several finite size exponents can be then extracted. Furthermore, universal critical behavior can be also established in terms of the bosonic Hilbert space truncation number, and the corresponding critical scaling exponents are found. Surprisingly, the critical correlation length exponents in terms of the photonic truncation number as well as the equivalently effective length scales are different in the the Rabi-Stark model and the quantum Rabi model, suggesting they belong to different universality classes. The second-order quantum phase transition is convincingly corroborated in the Rabi-Stark model at finite frequency ratios, by contrast, it only emerges at the infinite frequency ratio in the original quantum Rabi model without the Stark coupling.

In collaboration with Xiang-You Chen and You-Fei Xie.

**【邀请人】 高先龙 教授**

**欢迎老师和同学参加**